This work deals with the dielectric properties of silane treated pineapple leaf fiber and kenaf fiber reinforced phenolic hybrid composites. The aim of the present paper is to investigate the effect ...of silane treatment on the pineapple leaf fiber–kenaf fiber/matrix interfacial adhesion using the dielectric relaxation spectroscopy in the frequency range from 0.1 Hz to 1 MHz and temperature range from 50 to 180℃. Our hybrid composites were fabricated by hand lay-up method at 50% total fiber loading. All the results obtained were discussed in terms of dynamic molecular and interfacial process. Two interfacial polarizations identified as the Maxwell–Wagner–Sillars effect are observed. We note that silane treatment improved the interfacial adhesion between pineapple leaf fiber/kenaf fiber and phenolic resin and it will help to develop high performance kenaf fiber/pineapple leaf fiber reinforced polymer composites for industrial applications. In fact, as known, the silane treatment developed hydrophobic nature in pineapple leaf fiber and kenaf fiber which is very positive for fiber/matrix compatibility.
Natural rubber (NR) isolated from Hevea Brasiliens and reinforced with different amounts of cellulose nanowhiskers (extracted from the rachis of date palm tree) was investigated using differential ...scanning calorimetry and dielectric spectroscopy in the frequency range 0.1 Hz to 1 MHz, and the temperature range −80 to 200 °C. The experimental dielectric data were analysed within the formalisms of dielectric permittivity, complex conductivity and complex modulus. The results were discussed in terms of dc conductivity, interfacial polarization and electrode polarization. The paper aims to investigate especially the electrode polarization observed at low frequency and/or high temperature (LF/HT). It is exhibited that the understanding of the frequency space charge relaxation behaviour trapped close to the material/electrode interface will help one to elucidate the charge dynamics in the quasi static range. So charge carrier concentration and mobility in the sample at high temperature can be evaluated through the electrode polarization modeling of broadband dielectric spectroscopy data.
•Adding nanocellulose in latex led to composite with superior dielectric properties.•Dipolar relaxation, interfacial and electrode polarization are modeled.•The nanocomposites fragility parameters are estimated from relaxation process.•Close to material/electrode interface, charge dynamics are elucidated.•Charge carrier concentration and their mobility in nanocomposites are evaluated.
Summary
Local mechanical properties of submicron features are of particular interest due to their influence on macroscopic material performance and behaviour. This study is focused on local ...nanomechanical measurements, based on the latest Atomic Force Microscopy (AFM) mode, where the peak force set point is finely controlled at each pixel. After probe calibration, we evaluate the impact of spring constant of two AFM hand‐crafted natural full diamond tips with steel cantilevers, used for mapping. Based on the fast capture of the cantilever deflection at each pixel and real time force curve analysis in the elastic region, AFM local measured contact moduli mappings of the silica beads (>50 GPa) incorporated in an epoxy resin matrix, are compared with those determined using classical instrumented nanoindentation tests. Our analyses show that with the two AFM probes, without local residual deformation, the high moduli of the silica beads measured with this advanced AFM mode are within the standard deviation of the values determined by classical nanoindentation.
Lay Description
The knowledge of material properties at the nanometer scale is a key parameter for well understanding and determining the behavior of material at macroscopic scale. In this paper, we compare two methods (an advanced mode and a classical one) based on the analysis of probes in interaction with the surface of studied material. We focus on a latest developed mode for determining local mechanical properties with a very high spatial resolution. For the advanced mode, we also consider two different hand‐crafted probes. Our analyses show that with the high spatial resolution advanced mode, local mechanical properties are well determined. We also highlight the impact of the properties of the used probes for this advanced mode. In a final step, the power of the presented investigation lies in the fact that it does not modify the topography of the surface.
The dielectric properties of sugar palm fiber (SPF) reinforced-phenolic (PF) composites have been studied in terms of bonding between fiber and matrix. The paper aims to investigate the effect of ...alkaline treatment and sea water treatment on SPF composite using the dielectric relaxation spectroscopy in the frequency range from 0.1 Hz to 0.1 MHz and temperature range from 80 °C to 200 °C. The results were discussed in terms of dynamic molecular and interfacial process. Our analysis suggests that interfacial adhesion in the case of alkaline treated composite is higher than those of untreated and sea water treated composites.
•Adding treated fibers SPF led to composite with superior dielectric properties.•Dipolar relaxation and interfacial polarization are modelled.•The nanocomposites fragility parameters are estimated from relaxation process.•Comparison between sea water and alkaline treatment fibers is elucidated.•Dielectric strength and activated energy for different process are evaluated.
Dynamic dielectric properties of an isotactic polypropylene matrix grafted with maleic anhydride (CA 100) and then crosslinked by polyether amine molecules and reinforced with different weight ...percentages of graphite nanoplatelets (GNPs), KNG180, were studied for the first time and compared to those obtained by DMA (Dynamic Mechanical Analysis). The main objective of this work was to investigate the reinforcement effect of GNPs focusing on the GNPs/matrix interfacial adhesion using dynamic dielectric relaxation spectroscopy in the frequency range from 0.1 Hz to 1 MHz and temperature range from 20 to 140 °C. The obtained interfacial polarization increments
Δ
ε
MWS
from MWS (Maxwell Wagners Sillars) relaxation showed a threshold value of 3% in weight of KNG180. This analysis suggests that interfacial compatibility between matrix and fillers in the case of nanocomposite KNG180 3 wt% is higher than those of other nanocomposites. A new plasma treatment was used to modify graphite nano-fillers to produce different types of nanocomposites. The 5 wt% plasma treated graphite nanocomposite shows a good dispersion of the nano-fillers but also a high value of
Δ
ε
MWS
, which is an indication of high graphite/graphite interaction. This evolution could show that this material can be close to the formation of an electrical percolation network.
•Investigation of a swirled oxy-coal combustion.•Use of new experimental data set for flow and combustion properties.•Impact of numerical interphase treatment in both LES and RANS.•Analysis of ...turbulence modeling effect on devolatilization and coal burnout.
Numerical studies of pulverized coal swirl combustion in oxy-fuel atmosphere are carried out. Thereby two issues are especially addressed: (1) how LES and RANS impact differently the predictions of combustion properties even though, in both approaches, the same kinetic rates are used to represent the coal combustion processes; (2) how the numerical multiphase treatments may affect the prediction of micro-process interaction as well as the range in which these processes are not negligible. For that purpose a methodology is developed based on an Eulerian-Lagrangian oxy-coal combustion module which is designed relying on the state of the art models as implemented in the commercial code ANSYS Fluent 17. This especially includes three kinetic rates for the description of coal combustion, namely coal devolatilization, volatile combustion and char combustion. Based on an appropriate Stokes number consideration, a full two-way inter-phase coupling has been numerically adopted.
To assess the prediction capability of the overall model, a new set of experimental data from a 60kWth oxy-coal test facility is employed. First, the model validation is ensured by comparison of results in terms of flow field and products from volatile and char combustion. Then, an analysis is performed to elucidate how the two-phase turbulence modeling impacts the thermal flow predictions along with the evolution of multiphase oxy-coal combustion properties.
Finally, it is demonstrated how the numerical multiphase treatments affect the prediction of micro-process interaction in terms of coal devolatilization, coal particle distribution due to turbulent particle dispersion, and of gaseous heat release as well as char burnout. The range in which these interphase processes (subgrid scale particle dispersion) are not negligible is also pointed out in terms of subgrid scale Stokes number.
Bacteria glide across solid surfaces by mechanisms that have remained largely mysterious despite decades of research. In the deltaproteobacterium Myxococcus xanthus, this locomotion allows the ...formation stress-resistant fruiting bodies where sporulation takes place. However, despite the large number of genes identified as important for gliding, no specific machinery has been identified so far, hampering in-depth investigations. Based on the premise that components of the gliding machinery must have co-evolved and encode both envelope-spanning proteins and a molecular motor, we re-annotated known gliding motility genes and examined their taxonomic distribution, genomic localization, and phylogeny. We successfully delineated three functionally related genetic clusters, which we proved experimentally carry genes encoding the basal gliding machinery in M. xanthus, using genetic and localization techniques. For the first time, this study identifies structural gliding motility genes in the Myxobacteria and opens new perspectives to study the motility mechanism. Furthermore, phylogenomics provide insight into how this machinery emerged from an ancestral conserved core of genes of unknown function that evolved to gliding by the recruitment of functional modules in Myxococcales. Surprisingly, this motility machinery appears to be highly related to a sporulation system, underscoring unsuspected common mechanisms in these apparently distinct morphogenic phenomena.
Understanding the principles underlying the plasticity of signal transduction networks is fundamental to decipher the functioning of living cells. In Myxococcus xanthus, a particular chemosensory ...system (Frz) coordinates the activity of two separate motility systems (the A- and S-motility systems), promoting multicellular development. This unusual structure asks how signal is transduced in a branched signal transduction pathway. Using combined evolution-guided and single cell approaches, we successfully uncoupled the regulations and showed that the A-motility regulation system branched-off an existing signaling system that initially only controlled S-motility. Pathway branching emerged in part following a gene duplication event and changes in the circuit structure increasing the signaling efficiency. In the evolved pathway, the Frz histidine kinase generates a steep biphasic response to increasing external stimulations, which is essential for signal partitioning to the motility systems. We further show that this behavior results from the action of two accessory response regulator proteins that act independently to filter and amplify signals from the upstream kinase. Thus, signal amplification loops may underlie the emergence of new connectivity in signal transduction pathways.
Abstract
Background and Aims
Studies have shown that the incidence of severe COVID-19 pneumonia is higher in elderly patients and especially those with comorbidities including chronic kidney disease. ...The aim of our study was to determine risk factors for mortality in elderly chronic hemodialysis (HD) patients.
Method
We conducted a cross-sectional, observational, and analytical study, in the dialysis unit of the internal medicine department at Charles Nicolle Hospital over an 11-month period from September 2020 to August 2021. We studied the correlation between mortality and the different epidemiological, clinical and biological data via the SPSS software.
Results
We included 59 patients, with a mean age of 73 years 65-93 and a gender ratio of 1. All patients had confirmed COVID-19 infection, chronic kidney failure and required regular HD since at least 3 months. One on four patients had a coronary artery disease, 55% were diabetics and 72% had hypertension. From the 19 patients who underwent chest scan, 68% had severe lesions. Emergency HD had to be conducted for 25% of the patients, mainly because of hyperkalemia. At least one ongoing HD session was interrupted for neurologic, hemodynamic or respiratory instability in 26% of the patients. Mortality rate was 58%. Data that were associated with mortality in the univariate study were oxygen needs (p<10-3), COVID-19 infection severity (p=0.007), and interruption of HD session (p<10-3). Low blood pH levels and high pCo2 levels were also correlated to mortality (p=0.032 and p=0.020). Predictors of mortality in multivariate analysis were high oxygen needs (OR=1.368; 95% CI 1.081-1.732; P = .009), interruption of HD session (OR=1.426; 95% CI 1.070-1.846; P = .014) and severe form of COVID-19 infection (OR=1.770; 95% CI 1.062-2.980; P = .029).
Conclusion
According to these results, high oxygen needs, severity of COVID-19 infection and interruption of HD session represented risk factors of death in elderly patients undergoing chronic hemodialysis. As highlighted in previous studies, mortality rate in COVID-19 seems to be higher among elderly patients. However, diabetes and cardiovascular diseases were not identified as predictors of mortality in this sample of patients.
Chemosensory systems (CSS) are complex regulatory pathways capable of perceiving external signals and translating them into different cellular behaviors such as motility and development. In the ...δ-proteobacterium Myxococcus xanthus, chemosensing allows groups of cells to orient themselves and aggregate into specialized multicellular biofilms termed fruiting bodies. M. xanthus contains eight predicted CSS and 21 chemoreceptors. In this work, we systematically deleted genes encoding components of each CSS and chemoreceptors and determined their effects on M. xanthus social behaviors. Then, to understand how the 21 chemoreceptors are distributed among the eight CSS, we examined their phylogenetic distribution, genomic organization and subcellular localization. We found that, in vivo, receptors belonging to the same phylogenetic group colocalize and interact with CSS components of the respective phylogenetic group. Finally, we identified a large chemosensory module formed by three interconnected CSS and multiple chemoreceptors and showed that complex behaviors such as cell group motility and biofilm formation require regulatory apparatus composed of multiple interconnected Che-like systems.
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